Cleaning equipment and cleaning method

ABSTRACT

The present invention provides a cleaning equipment provided with a cleaning solution tank, a cleaning solution supply route for supplying the cleaning solution stored in the cleaning solution tank to a cleaning bath, a cleaning solution return route for returning the cleaning solution that has been supplied to the cleaning bath to the cleaning solution tank, a gas supply route for supplying a purge gas into the cleaning solution tank, and a gas discharge route for discharging the purge gas from the cleaning solution tank. Moreover, a cleaning solution discharge opening of the cleaning solution return route is immersed in the cleaning solution stored in the cleaning solution tank.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to cleaning equipments having asystem for circulating cleaning solution and cleaning methods using thesame, and in particular relates to cleaning equipments and cleaningmethods in which a volatile cleaning solution including an organicsolvent or the like is used to perform cleaning of a semiconductorsubstrate or a glass substrate, for example.

[0002] In the cleaning step of manufacturing processes for semiconductordevices, for example, a substrate cleaning equipment having a system forcirculating cleaning solution may be used. As for the schematicconfiguration of a batch-type spin cleaner for wafer, for example, suchcleaners include a cleaning solution tank for storing cleaning solutionand adjusting the temperature of the cleaning solution, and a chamber(cleaning bath) in which cleaning of a semiconductor substrate or thelike is carried out.

[0003] If a volatile cleaning solution containing an organic solvent,for example, is used, then the component that is volatilized from thecleaning solution is present in the space above the liquid surface ofthe cleaning solution that is stored in the cleaning solution tank.Accordingly, an inert gas such as nitrogen is constantly supplied intothe cleaning solution tank as a purge gas in order to prevent accidentssuch as the volatilized component igniting and exploding. Morespecifically, 5 to 25 L (liter) of an inert gas such as helium, argon,or nitrogen is supplied per minute to a cleaning solution tank having a10 to 40 L capacity.

[0004]FIG. 5 shows the pipe structure of an ordinary batch-type spincleaner for wafer.

[0005] As shown in FIG. 5, a cleaning solution 2 that is supplied into acleaning bath 1 in which the cleaning of an object to be cleaned, suchas a semiconductor substrate (not shown), is carried out is stored in acleaning solution tank 3. To the cleaning tank 3 are attached athermometer 4 for measuring the temperature of the cleaning solution 2and a heat source 5 for heating the cleaning solution 2. That is, thecleaning solution 2 is maintained at a predetermined temperature by afeedback control using the thermometer 4 and the heat source 5, and thusthe temperature of the cleaning solution 2 is controlled. If thecleaning solution 2 is volatile and the volatilized component from thecleaning solution 2 is ignitable, then an inert gas, as a purge gas, isflowed into a space 6 of the cleaning tank 3 from a gas supply pipe 7 inorder to prevent the ignition and explosion of the volatilized componentthat is present in the space 6 above the liquid surface of the cleaningsolution 2 that is stored in the cleaning solution tank 3. The inert gasand the volatilized component are discharged from the space 6 of thecleaning solution tank 3 via a gas discharge pipe 8. Thus, thevolatilized component of the cleaning solution 2 is purged from thecleaning solution tank 3.

[0006] Also, as shown in FIG. 5, the cleaning solution 2 is firstpressurized and pumped by a pump 9 on the cleaning solution 2 supplyroute from the cleaning solution tank 3 to the cleaning bath 1. Thecleaning solution 2 subsequently passes through a filter 10 for removingforeign matters such as particles, a flow meter 11 for controlling theflow of the cleaning solution 2, and a valve 12 for switching the routeof the cleaning solution 2, after which the cleaning solution 2 isexpelled toward the object to be cleaned, such as a semiconductorsubstrate (not shown), arranged inside the cleaning bath 1 from a nozzle(not shown) attached to an upper portion the cleaning bath 1. Then,after the cleaning solution 2 has been applied to the object to becleaned inside the cleaning bath 1, the cleaning solution 2 isdischarged from the cleaning bath 1 through a drain (not shown) providedat a bottom portion the cleaning bath 1, and is returned to cleaningsolution tank 3. That is, substrate cleaning is performed using acleaning solution 2 that is circulated in the substrate cleaningequipment shown in FIG. 5.

[0007] It should be noted that during substrate cleaning (that is, whenthe equipment is in operation) the valve 12 opens a route over which thecleaning solution 2 is supplied to the cleaning bath 1, shown by thesolid line, whereas when the device is in standby, the valve 12 opens aflow route for the cleaning solution 2, shown by the dashed line, overwhich the cleaning solution 2 is returned to the cleaning solution tank3 without passing through the cleaning bath 1.

[0008] However, when the above-described conventional substrate cleaningequipment is used, the cleaning solution performance, that is, itscleaning ability, drops sooner than anticipated, and as a result,foreign matters such as particles adhered to the substrate are notremoved and remain where they are, and this causes the problem of anincreased defect density and thus diminished yield of the semiconductordevices, for example. On the other hand, frequently exchanging thecleaning solution so as to maintain the performance of the cleaningsolution results in the problem of increased running costs for thecleaning solution. Also, in this case, it is necessary to stop thecleaning equipment when the cleaning solution is changed, which resultsin the problem of a drop in the productivity of the cleaning equipment.

SUMMARY OF THE INVENTION

[0009] In light of the foregoing, if a cleaning equipment having asystem in which cleaning solution is circulated is used, it is an objectof the present invention to obtain an excellent cleaning ability whilekeeping down costs related to the cleaning solution and increasing theproductivity of the cleaning equipment by reducing the frequency atwhich the cleaning solution is exchanged and preventing deterioration ofcleaning solution performance.

[0010] To achieve the foregoing objects, the inventors of the presentapplication examined the cause of the premature drop in cleaningsolution performance that occurs when conventional substrate cleaningequipments are used, and arrived at the following findings.

[0011]FIG. 6 illustrates the problematic aspects of conventionalsubstrate cleaning equipments, and more particularly illustrates theproblematic aspects of conventional cleaning solution tanks.

[0012] As shown in FIG. 6, a cleaning solution 52 that is stored insidea cleaning solution tank 51 is supplied from an outlet 53 provided inthe bottom portion of the cleaning solution tank 51 to a cleaning bath(not shown) via a cleaning solution supply pipe 54. At this time, thecleaning solution 52 is pressurized and pumped by a pressure pump 55that is provided in the cleaning solution supply pipe 54. On the otherhand, the cleaning solution 52 that has been supplied into the cleaningbath is returned into the cleaning solution tank 51 from a cleaningsolution discharge opening 57 that is provided in the ceiling portion ofthe cleaning solution tank 51 via a cleaning solution return pipe 56.Thus, cleaning is carried out by circulating the cleaning solution 52. Athermometer 58 and a heat source 59 are provided on the cleaningsolution tank 51, and through a feedback control using the thermometer58 and the heat source 59, the temperature of the cleaning solution 52is adjusted.

[0013] Also, as shown in FIG. 6, there is a space 60 above the liquidsurface of the cleaning solution 52 that is stored in the cleaningsolution tank 51, or put differently, between the liquid surface of thecleaning solution 52 that is stored in the cleaning solution tank 51 andthe ceiling portion of the cleaning solution tank 51. If the cleaningsolution 52 is volatile and the component volatilized from the cleaningsolution 52 is ignitable, then an inert gas serving as a purge gas isflowed from a gas supply opening 62 that is provided in the ceilingportion of the cleaning solution tank 51 into the space 60 via a gassupply pipe 61 in order to prevent the volatilized component that ispresent in the space 60 inside the cleaning solution tank 51 fromigniting and exploding. On the other hand, the inert gas that isintroduced into the space 60 and the volatilized component aredischarged from a gas discharge opening 63 provided in the ceilingportion of the cleaning solution tank 51 via a gas discharge pipe 64. Atthis time, the volatilization of components included in the cleaningsolution 52 (hereinafter, referred to as “specific components”) ispromoted by the introduction of the inert gas into the cleaning solutiontank 51. The reason for this is that the concentration of specificcomponents in the cleaning solution 52 that is stored in the cleaningsolution tank 51 and the concentration of specific componentsvolatilized from the cleaning solution 52 in the space 60 are maintainedat a constant equilibrium. Consequently, the greater the area of contactbetween the cleaning solution 52 and the inert gas inside the cleaningsolution tank 51, the more the volatilization of specific componentsincluded in the cleaning solution 52 is facilitated.

[0014] Incidentally, in conventional substrate cleaning equipments, thecleaning solution 52 (dotted region of FIG. 6) that has been dischargedfrom the cleaning solution discharge opening 57 via the cleaningsolution return pipe 56 flows through the space 60 in a stream or acylindrical fashion. For that reason, the contact area between thecleaning solution 52 and the inert gas inside the cleaning solution tank51 becomes the total of the contact area between the cleaning solution52 that is stored in the cleaning solution tank 51 and the inert gas andthe contact area between the inert gas and the cleaning solution 52 thatflows through the space 60 in a stream or cylindrical fashion. As aresult there is noticeable volatilization of specific components fromthe cleaning solution 52, and as a result there is a danger that theperformance of the cleaning solution 52 will drop. This danger becomesincreasingly conspicuous if the usage temperature of the cleaningsolution 52 is set at or above room temperature, and particularly if thecleaning solution 52 is used at an elevated temperature of about 50 to100° C.

[0015] In the above-described conventional substrate cleaning equipment,the cleaning solution performance, that is, its cleaning ability, dropsin a shorter period than expected because a large volume of specificcomponents included in the cleaning solution is volatilized, and as aresult, foreign matters such as particles adhered to the substrate arenot removed and remain on the substrate, and this causes increaseddefect density and thus a diminished yield of semiconductor devices. Onthe other hand, if the cleaning solution is frequently exchanged inorder to maintain the performance of the cleaning solution, then thisconversely results in an increase in running costs for the cleaningsolution and diminished productivity of the cleaning equipment.

[0016] From these circumstances, the inventors of the presentapplication concluded that to achieve the objects of the presentinvention it is imperative that fluctuations in the cleaning solutioncomposition are inhibited so as to stabilize the cleaning solutioncomposition by inhibiting the volatilization of cleaning solutioncomponents in the cleaning solution tank of a cleaning equipment thathas a system for circulating cleaning solution, or in other words, byinhibiting volatilization of cleaning solution components caused bycontact between the purge gas that is introduced into the cleaningsolution tank and the cleaning solution. Accordingly, the inventors ofthe present application arrived at the following cleaning equipments andcleaning methods.

[0017] More specifically, a cleaning equipment according to the presentinvention is provided with a cleaning solution tank for storing acleaning solution, a cleaning bath in which cleaning of an object to becleaned is carried out using the cleaning solution, a cleaning solutionsupply route for supplying the cleaning solution stored in the cleaningsolution tank to the cleaning bath, a cleaning solution return route forreturning the cleaning solution supplied to the cleaning bath to thecleaning solution tank, a gas supply route for supplying a purge gasinto the cleaning solution tank, and a gas discharge route fordischarging the purge gas from the cleaning solution tank, and acleaning solution discharge opening of the cleaning solution returnroute is immersed in the cleaning solution that is stored in thecleaning solution tank.

[0018] According to the cleaning equipment of the present invention, thecleaning solution discharge opening of the cleaning solution returnroute for returning the cleaning solution to the cleaning solution tankis immersed in the cleaning solution that is stored in the cleaningsolution tank. Put differently, the cleaning solution discharge openingis positioned below the liquid surface of the cleaning solution that isstored in the cleaning solution tank, and thus the problem, seen withconventional cleaning equipments in which the cleaning solutiondischarge opening is provided in the ceiling portion of the cleaningsolution tank, of the cleaning solution that is discharged from thecleaning solution discharge opening dropping in a stream or acylindrical manner through the space above the liquid surface of thecleaning solution that is stored in the cleaning solution tank isavoided. Put differently, the cleaning solution that is released fromthe cleaning solution discharge opening can be kept from coming intocontact with the purge gas that is introduced into the cleaning solutiontank. As a result, the area of contact between the cleaning solution andthe inert gas within the cleaning solution tank can be reduced, and thusvolatilization of cleaning solution components can be inhibited.Consequently, fluctuations in the cleaning solution composition areinhibited so that the cleaning solution composition can be stabilized,and thus cleaning solution performance, that is, its cleaning ability,can be kept from deteriorating. In addition, the frequency at which thecleaning solution is changed can be reduced because inhibitingvolatilization of cleaning solution components allows the cleaningsolution to be used for longer periods. Therefore, costs related to thecleaning solution can be kept down and the operation ratio of thecleaning equipment in production line can be increased, so thatproduction costs can be significantly reduced.

[0019] In the cleaning equipment of the present invention, it ispreferable that the gas supply route has a first valve for restricting afrequency at which the purge gas is supplied.

[0020] Thus, by using the first valve to lower the frequency at whichthe purge gas is supplied, the frequency at which the purge gas and thecleaning solution come into contact inside the cleaning solution tankcan be reduced. Thus, volatilization of cleaning solution components,that is, fluctuations in the cleaning solution composition, can beinhibited even further, and thus the cleaning solution composition canbe further stabilized.

[0021] In addition, in this case, the first valve can be anelectromagnetic valve.

[0022] In the cleaning equipment of the present invention, it ispreferable that the gas discharge route has a second valve forrestricting the volume of discharged purge gas.

[0023] Thus, by using the second valve to lower the volume of purge gasthat is discharged, the purge gas inside the cleaning solution tank ispressurized and thus the volume of volatilized (vaporized) cleaningsolution components can be reduced even further. Consequently,fluctuations in the cleaning solution composition can be reduced evenfurther and the cleaning solution composition can be further stabilized,so that deterioration of the cleaning ability can be more reliablyprevented. Also, by further inhibiting the volatilization of cleaningsolution components, the usage period of the cleaning solution can beextended even longer, and thus the frequency at which the cleaningsolution must be exchanged can be reduced even more and therefore costsrelated to the cleaning solution can be further reduced.

[0024] In addition, in this case, the second valve can be a pressureregulating valve.

[0025] In the cleaning equipment of the present invention, it ispreferable that the cleaning solution supply route has a pressure pumpfor pressurizing and supplying the cleaning solution.

[0026] Thus, the cleaning solution that is stored in the cleaningsolution tank can be reliably supplied to the cleaning bath.

[0027] In the cleaning equipment of the present invention, if thecleaning solution that is stored in the cleaning solution tank is avolatile cleaning solution containing an organic solvent or the like,then the above effects become readily apparent.

[0028] In the cleaning equipment of the present invention, it ispreferable that an inert gas such as helium, argon, or nitrogen is usedas the purge gas.

[0029] In the cleaning equipment of the present invention, if the objectto be cleaned is for example a semiconductor substrate or a glasssubstrate, that is, if the cleaning equipment of the present inventionis a substrate cleaning equipment, then the above effects becomeparticularly apparent. In this case, it is preferable that the substratecleaning equipment is a batch-type or a single-wafer-type spin cleaningequipment.

[0030] A cleaning method according to the present invention includes afirst step of supplying a cleaning solution that is stored in a cleaningsolution tank into a cleaning bath in which cleaning of an object to becleaned is carried out, a second step of returning the cleaning solutionthat has been supplied into the cleaning bath to the cleaning solutiontank, a third step of supplying a purge gas to the cleaning solutiontank, and a fourth step of discharging the purge gas from the cleaningsolution tank, wherein the second step is performed using a cleaningsolution return route having a cleaning solution discharge openingimmersed in the cleaning solution that is stored in the cleaningsolution tank.

[0031] According to the cleaning method of the present invention, thesame effects as the cleaning equipment of the present invention areobtained because the method is a cleaning method in which the cleaningequipment of the present invention is used.

[0032] In the cleaning method of the present invention, it is preferablethat the third step includes a step of reducing a frequency at which thepurge gas is supplied.

[0033] Thus, volatilization of cleaning solution components, that is,fluctuations in the cleaning solution composition, can be inhibited evenfurther because the frequency at which the purge gas and the cleaningsolution come into contact inside the cleaning solution tank can bereduced, and thus the cleaning solution composition can be furtherstabilized.

[0034] In the cleaning method of the present invention, it is preferablethat the fourth step includes a step of reducing the volume ofdischarged purge gas.

[0035] Thus, volatilization of cleaning solution components, that is,fluctuations in the cleaning solution composition, can be inhibited evenfurther because the purge gas inside the cleaning solution tank can bepressurized, and thus the cleaning solution composition can be furtherstabilized so that deterioration of the cleaning ability can be morereliably prevented. Also, by further inhibiting volatilization of thecleaning solution components, the usage period of the cleaning solutioncan be maintained even longer, so that the frequency at which thecleaning solution must be changed can be even further reduced andtherefore costs pertaining to the cleaning solution can be reducedfurther.

[0036] In the cleaning method of the present invention, if the cleaningsolution that is stored in the cleaning solution tank is a volatilecleaning solution that contains an organic solvent or the like, then theabove effects become more apparent.

[0037] In the cleaning method of the present invention, it is preferablethat an inert gas such as helium, argon, or nitrogen is used as thepurge gas.

[0038] In the method device of the present invention, if the object tobe cleaned is for example a semiconductor substrate or a glasssubstrate, that is, if the cleaning method of the present invention is asubstrate cleaning method, then the above effects become particularlyapparent. In this case, it is preferable that the substrate cleaningequipment is a batch-type or a single-wafer-type spin cleaningequipment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is shows the configuration of the cleaning equipmentaccording to Embodiment 1 of the present invention.

[0040]FIG. 2 is shows the configuration of the cleaning equipmentaccording to Embodiment 2 of the present invention.

[0041]FIG. 3 is shows the configuration of the cleaning equipmentaccording to Embodiment 3 of the present invention.

[0042]FIG. 4 shows the total cleaning solution exchange frequency forthe cleaning equipments according to Embodiments 1 to 3 of the presentinvention in a case where a representative volatile cleaning solution isused at a temperature of 70° C.

[0043]FIG. 5 shows the pipe structure of a general spin-type batchsemiconductor cleaning equipment.

[0044]FIG. 6 shows the problematic aspects of a conventionalsemiconductor cleaning equipment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Embodiment 1

[0046] Hereinafter, the cleaning equipment and the cleaning methodaccording to Embodiment 1 of the present invention are described withreference to the drawings. It should be noted that the cleaningequipment according to Embodiment 1 is a cleaning equipment having asystem for circulating cleaning solution like that shown in FIG. 5, forexample.

[0047]FIG. 1 shows the configuration of a cleaning equipment accordingto Embodiment 1, and more specifically shows the configuration of thecleaning solution tank and surrounding elements of a cleaning equipmentaccording to Embodiment 1.

[0048] As shown in FIG. 1, an end of a cleaning solution supply pipe 104for supplying cleaning solution 102 into a cleaning bath (not shown) inwhich cleaning of an object to be cleaned is carried out is attached toan outlet 103 provided in the bottom portion of a cleaning solution tank101 for storing the cleaning solution 102. The other end of the cleaningsolution supply pipe 104 is connected to the cleaning bath and alsoprovided with a pressure pump 105 proximate to the outlet 103 of thecleaning solution supply pipe 104.

[0049] In addition, a cleaning solution return pipe 106 for returningthe cleaning solution 102 that has been supplied into the cleaning bathback into the cleaning solution tank 101 is connected to the cleaningsolution tank 101. Here, the cleaning solution return pipe 106 passesthrough the ceiling portion of the cleaning solution tank 101, and acleaning solution discharge opening 107, which is one end of thecleaning solution return pipe 106, is immersed in the cleaning solution102 that is stored in the cleaning solution tank 101. It should be notedthat in this embodiment there are no particular limitations to where thecleaning solution return pipe 106 penetrates into the cleaning solutiontank 101.

[0050] Furthermore, a thermometer 108 for measuring the temperature ofthe cleaning solution 102 and a heat source 109 for heating the cleaningsolution 102 are attached to the cleaning solution tank 101. A space 110is provided above the liquid surface of the cleaning solution 102 thatis stored in the cleaning solution tank 101, that is, between the liquidsurface of the cleaning solution 102 that is stored in the cleaningsolution tank 101 and the ceiling portion of the cleaning solution tank101. In addition, an end of a gas supply pipe 111 for supplying inertgas as a purge gas into the space 110 of the cleaning solution tank 101is attached to a gas supply opening 112 provided in the ceiling portionof the cleaning solution tank 101. Moreover, an end of a gas dischargepipe 114 for discharging the inert gas from the space 110 of thecleaning solution tank 101 is attached to a gas discharge opening 113provided in the ceiling portion of the cleaning solution tank 101. Itshould be noted that in the present embodiment, helium, argon, ornitrogen, for example, can be used as the inert gas that is introducedinto the cleaning solution tank 101.

[0051] A description of the operation of the cleaning equipmentaccording to Embodiment 1 and shown in FIG. 1 follows.

[0052] First, the cleaning solution 102 stored inside the cleaningsolution tank 101 is supplied from the outlet 103 in the bottom portionof the cleaning solution tank 101 to the cleaning bath (not shown) viathe cleaning solution supply pipe 104. At this time, the cleaningsolution is pressurized and pumped by the pressure pump 105. On theother hand, the cleaning solution 102 that has been supplied into thecleaning bath is passed through the cleaning solution return pipe 106and returned into the cleaning solution tank 101 from the cleaningsolution discharge opening 107. In the present embodiment, cleaning ofthe object to be cleaned is carried out by circulating the cleaningsolution 102 in this way. In addition, the temperature of the cleaningsolution 102 is adjusted through a feedback control in which thethermometer 108 and the heat source 109 that are attached to thecleaning solution tank 101 are used. If the cleaning solution 102 isvolatile and the component volatilized from the cleaning solution 102 isignitable, then an inert gas is delivered from the gas supply opening112 into the space 110 via the gas supply pipe 111 in order to preventthe volatilized component in the space 110 inside the cleaning solutiontank 101 from igniting and exploding. On the other hand, the inert gasthat is introduced into the space 110 and the volatilized component aredischarged from the gas discharge pipe 114 via the gas discharge opening113.

[0053] As explained above, according to Embodiment 1, the cleaningsolution discharge opening 107 of the cleaning solution return pipe 106for returning the cleaning solution 102 to the cleaning solution tank101 is immersed in the cleaning solution 102 stored in the cleaningsolution tank 101. That is, the cleaning solution discharge opening 107is located below the liquid surface of the cleaning solution 102 storedin the cleaning solution tank 101, and thus the cleaning solution 102that is discharged from the cleaning solution discharge opening 107 canbe kept from falling in a stream or a cylindrical fashion through thespace 110 inside the cleaning solution tank 101. In other words, thecleaning solution 102 that is released through the cleaning solutiondischarge opening 107 can be kept from coming into contact with thepurge gas that is introduced into the cleaning solution tank 101. As aresult, the area of contact between the cleaning solution 102 and theinert gas inside the cleaning solution tank 101 can be reduced, so thatvolatilization of cleaning solution components can be inhibited.Consequently, fluctuations in the cleaning solution composition areinhibited so that the cleaning solution composition can be stabilized,and thus deterioration of cleaning solution 102 performance, that is,its cleaning ability, can be prevented. In addition, by inhibitingvolatilization of cleaning solution components, the period of time thatthe cleaning solution 102 can be used is extended, and thus thefrequency at which the cleaning solution 102 must be changed can bereduced. Therefore, costs associated with the cleaning solution 102 canbe kept down and the operation ratio of the cleaning equipment inproduction line can be increased, so that production costs can besignificantly reduced.

[0054] The above effects are particularly conspicuous if, in Embodiment1, substrate cleaning of a semiconductor substrate or a glass substrate,for example, is carried out using a volatile cleaning solution thatcontains an organic solvent or the like. In this case, it is preferablethat the substrate cleaning equipment is a batch-type or asingle-wafer-type spin cleaning equipment.

[0055] Embodiment 2

[0056] Hereinafter, the cleaning equipment and the cleaning methodaccording to Embodiment 2 of the present invention are described withreference to the drawings. It should be noted that the cleaningequipment according to Embodiment 2 is a cleaning equipment having asystem for circulating cleaning solution like that shown in FIG. 5, forexample.

[0057]FIG. 2 schematically shows the configuration of a cleaningequipment according to Embodiment 2, and more specifically schematicallyshows the configuration of the cleaning solution tank and surroundingelements of a cleaning equipment according to Embodiment 2. It should benoted that in FIG. 2, elements that are identical to those of thecleaning equipment according to Embodiment 1 shown in FIG. 1 have beenassigned identical reference numerals and a description thereof has beenomitted.

[0058] As shown in FIG. 2, the cleaning equipment according toEmbodiment 2 differs from that according to Embodiment 1 in that the gassupply pipe 111 for supplying inert gas as a purge gas to the cleaningsolution tank 101 has a first valve 120 for restricting the frequency atwhich inert gas is supplied. An electromagnetic valve or the like can beemployed as the first valve 120. Also, the first valve 120 is forexample provided proximate to the gas supply opening 112 in the gassupply pipe 111. As an example of a specific opening/closing method forthe first valve 120, the first valve 120 can be closed when theequipment is in operation (during cleaning operation: if a cleaningequipment like that shown in FIG. 5 with a system for circulatingcleaning solution, the time during which the route for supplyingcleaning solution to the cleaning bath 1, shown by the solid line, isopen), whereas the first valve 120 can be open during equipment standby(if the cleaning equipment shown the FIG. 5, then this is the timeduring which the route shown by the dashed line is open so that thecleaning solution 2 is circulated without passing through the cleaningbath 1).

[0059] According to Embodiment 2, the following effect can be obtainedin addition to the effects of Embodiment 1. That is, by using the firstvalve 120 to lower the frequency at which inert gas is supplied to thecleaning solution tank 101, the frequency at which the inert gas and thecleaning solution 102 come into contact inside the cleaning solutiontank 101 can be reduced. Thus, volatilization of cleaning solutioncomponents, that is, fluctuations in the cleaning solution composition,can be even further inhibited, so that the cleaning solution compositioncan be further stabilized, and therefore deterioration of its cleaningability can be more reliably prevented.

[0060] The above effects are particularly conspicuous if, in Embodiment2, substrate cleaning of a semiconductor substrate or a glass substrate,for example, is carried out using a volatile cleaning solution thatcontains an organic solvent or the like. In this case, it is preferablethat the substrate cleaning equipment is a batch-type or asingle-wafer-type spin cleaning equipment.

[0061] Embodiment 3

[0062] Hereinafter, the cleaning equipment and the cleaning methodaccording to Embodiment 3 of the present invention are described withreference to the drawings. It should be noted that the cleaningequipment according to Embodiment 3 is a cleaning equipment having asystem for circulating cleaning solution like that shown in FIG. 5, forexample.

[0063]FIG. 3 schematically shows the configuration of a cleaningequipment according to Embodiment 3, and more specifically schematicallyshows the configuration of the cleaning solution tank and surroundingelements of a cleaning equipment according to Embodiment 3. It should benoted that in FIG. 3, elements that are identical to those of thecleaning equipment according to Embodiment 1 shown in FIG. 1 have beenassigned identical reference numerals and a description thereof has beenomitted.

[0064] As shown in FIG. 3, the first aspect in which the cleaningequipment according to Embodiment 3 differs from that according toEmbodiment 1 is that the gas supply pipe 111 for supplying inert gas asa purge gas to the cleaning solution tank 101 has a first valve 120 forrestricting the frequency at which inert gas is supplied. Anelectromagnetic valve or the like can be employed as the first valve120. Also, the first valve 120 is for example provided proximate to thegas supply opening 112 in the gas supply pipe 111. As an example of aspecific opening/closing method for the first valve 120, the first valve120 can be closed when the equipment is in operation, whereas the firstvalve 120 can be open when the equipment is in standby.

[0065] Moreover, as shown in FIG. 3, a second aspect in which thecleaning equipment according to Embodiment 3 differs from that accordingto Embodiment 1 is that the gas discharge pipe 114 for discharging inertgas from the cleaning solution tank 101 has a second valve 130 forrestricting the discharged volume of inert gas, that is, purge gas. Apressure regulating valve or the like can be employed as the secondvalve 130. Also, the second valve 130 is for example provided proximateto the gas discharge opening 113 in the gas discharge pipe 114.Moreover, in this embodiment, a pressure sensor 131 is provided betweenthe gas supply opening 112 and the first valve 120 in the gas supplypipe 111 in order to measure the pressure of the inert gas inside thecleaning solution tank 101. Thus, in this embodiment, the pressure ofthe inert gas inside the cleaning solution tank 101 can be set higherthan atmospheric pressure and maintained using the second valve 130 andthe pressure sensor 131.

[0066] As explained above, according to Embodiment 3, the following twoeffects can be obtained in addition to the effects of Embodiment 1.

[0067] First, like Embodiment 2, by using the first valve 120 to lowerthe frequency at which inert gas is supplied to the cleaning solutiontank 101, the frequency at which the inert gas and the cleaning solution102 come into contact inside the cleaning solution tank 101 can bereduced. Thus, volatilization of cleaning solution components, that is,fluctuations in the cleaning solution composition, can be even furtherinhibited, so that the cleaning solution composition can be furtherstabilized and therefore deterioration of its cleaning ability can bemore reliably prevented.

[0068] In addition, by using the second valve 130 to reduce the volumeof discharged inert gas, the inert gas inside the cleaning solution tank101 can be pressurized and therefore the volume of volatilized(vaporized) cleaning solution components can be further inhibited.Consequently, fluctuations in the cleaning solution composition can beinhibited even further so that the cleaning solution composition can befurther stabilized, and thus deterioration of the cleaning ability canbe more reliably reduced. Also, by further inhibiting volatilization ofcleaning solution components, the usage period of the cleaning solution102 can be maintained longer, and thus the frequency at which thecleaning solution 102 must be changed can be reduced even more, so thatcosts associated with the cleaning solution 102 can be further reduced.

[0069] The above effects are particularly conspicuous if, in Embodiment3, substrate cleaning of a semiconductor substrate or a glass substrate,for example, is carried out using a volatile cleaning solution thatcontains an organic solvent or the like. In this case, it is preferablethat the substrate cleaning equipment is a batch-type or asingle-wafer-type spin cleaning equipment.

[0070] It should be noted that in Embodiment 3, the pressure of theinert gas in the cleaning solution tank 101 is preferably set to apressurized state of about 105 to 120 kPa, in contrast to atmosphericpressure at 101.3 kPa. Also, the period during which this pressurizedstate is maintained can be the period of device standby, which is whenthe first valve 120 is open. Alternatively, the opening and closing ofthe first valve 120 can be controlled so that the above pressurizedstate is maintained without regard to whether the equipment is inoperation or standby.

[0071]FIG. 4 shows the frequency (hereinafter, referred to as the totalcleaning solution exchange frequency) at which the cleaning solution(all cleaning solution in the circulation system) must be exchanged perday in order to sustain the cleaning ability in a case where arepresentative volatile cleaning solution is used at a temperature of70° C. in the cleaning equipments according to Embodiments 1 to 3. Itshould be noted that FIG. 4 also shows the total cleaning solutionexchange frequency of the conventional cleaning equipment shown in FIG.6 as a conventional example in a case where the same volatile cleaningsolution is used at the same temperature.

[0072] As shown in FIG. 4, the usage period (period from when thecleaning solution is exchanged once to when it is exchanged next) of thecleaning solution in each embodiment is longer than that for thecomparative example, and more particularly, the usage period of thecleaning solution in Embodiment 3 is longest. This is due to combinedeffect of the cleaning solution component volatilization preventioneffect of Embodiment 1 due to the reduction of contact area between theinert gas and the cleaning solution 102 in the cleaning solution tank101 because the cleaning solution 102 is kept from flowing from thecleaning solution discharge opening 107 into the space 110 in a stream,for example, the cleaning solution component volatilization preventioneffect of Embodiment 2 due to the reduction of the frequency of contactbetween the inert gas and the cleaning solution 102 in the cleaningsolution tank 101 because the frequency at which the inert gas issupplied into the cleaning solution tank 101 is reduced, and thecleaning solution component volatilization prevention effect ofEmbodiment 3 due to the reduction of the volume of discharged inert gasso as to keep the inert gas inside the cleaning solution tank 101 in apressurized state.

[0073] The invention may be embodied in other forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not limiting. The scope of the invention is indicatedby the appended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A cleaning equipment comprising: a cleaningsolution tank for storing a cleaning solution; a cleaning bath in whichcleaning of an object to be cleaned is carried out using the cleaningsolution; a cleaning solution supply route for supplying the cleaningsolution stored in the cleaning solution tank to the cleaning bath; acleaning solution return route for returning the cleaning solution thathas been supplied to the cleaning bath to the cleaning solution tank; agas supply route for supplying a purge gas into the cleaning solutiontank; and a gas discharge route for discharging the purge gas from thecleaning solution tank; wherein a cleaning solution discharge opening ofthe cleaning solution return route is immersed in the cleaning solutionthat is stored in the cleaning solution tank.
 2. The cleaning equipmentaccording to claim 1, wherein the gas supply route has a first valve forrestricting a frequency at which the purge gas is supplied.
 3. Thecleaning equipment according to claim 2, wherein the first valve is anelectromagnetic valve.
 4. The cleaning equipment according to claim 1,wherein the gas discharge route has a second valve for restricting thevolume of discharged purge gas.
 5. The cleaning equipment according toclaim 4, wherein the second valve is a pressure regulating valve.
 6. Thecleaning equipment according to claim 1, wherein the cleaning solutionsupply route has a pressure pump for pressurizing and supplying thecleaning solution.
 7. The cleaning equipment according to claim 1,wherein the cleaning solution stored in the cleaning solution tank is avolatile cleaning solution.
 8. The cleaning equipment according to claim7, wherein the volatile cleaning solution contains an organic solvent.9. The cleaning equipment according to claim 1, wherein the purge gas isan inert gas.
 10. The cleaning equipment according to claim 1, whereinthe object to be cleaned is a semiconductor substrate or a glasssubstrate.
 11. The cleaning equipment according to claim 10, wherein thecleaning bath is a cleaning bath of a batch-type or a single-wafer-typespin cleaning equipment.
 12. A cleaning method comprising: a first stepof supplying a cleaning solution that is stored in a cleaning solutiontank into a cleaning bath in which cleaning of an object to be cleanedis carried out; a second step of returning the cleaning solution thathas been supplied into the cleaning bath to the cleaning solution tank;a third step of supplying a purge gas to the cleaning solution tank; anda fourth step of discharging the purge gas from the cleaning solutiontank; wherein the second step is performed using a cleaning solutionreturn route having a cleaning solution discharge opening immersed inthe cleaning solution that is stored in the cleaning solution tank. 13.The cleaning method according to claim 12, wherein the third stepincludes a step of reducing a frequency at which the purge gas issupplied.
 14. The cleaning method according to claim 13, wherein thefourth step includes a step of reducing the volume of discharged purgegas.
 15. The cleaning method according to claim 12, wherein the cleaningsolution that is stored in the cleaning solution tank is a volatilecleaning solution.
 16. The cleaning method according to claim 15,wherein the volatile cleaning solution contains an organic solvent. 17.The cleaning method according to claim 12, wherein the purge gas is aninert gas.
 18. The cleaning method according to claim 12, wherein theobject to be cleaned is a semiconductor substrate or a glass substrate.19. The cleaning method according to claim 18, wherein the cleaning bathis a cleaning bath of a batch-type or a single-wafer-type spin cleaningequipment.